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SINGAPORE — More than a third of mammal species considered extinct or missing have been rediscovered, a study says, and a lot of effort is wasted in trying to find species that have no chance of being found again.

Species face an accelerated rate of extinction because of pollution, climate change, habitat loss and hunting, and this rate of loss is putting ecosystems and economies at ever greater risk, according to the United Nations.

Researchers at the University of Queensland in Australia said a greater understanding of patterns of extinction could channel more resources to finding and protecting species listed as missing before it's too late.

"In the past people have been very happy to see individual species found again, but they haven't looked at the bigger picture and realized that it's not random," university research fellow Diana Fisher, lead author of the study, told Reuters.

Fisher and her colleague Simon Blomberg studied data on rediscovery rates of missing mammals to see if extinction from different causes is equally detectable. They also wanted to see which factors affected the probability of rediscovery.

They found that species affected by habitat loss were much more likely to be misclassified as extinct or to remain missing than those affected by introduced predators and diseases.

"It is most likely that the highest rates of rediscovery will come from searching for species that have gone missing during the twentieth century and have relatively large ranges threatened by habitat loss," they say in the report in the Proceedings of the Royal Society B journal.

The United Nations hosts a major meeting in Japan next month at which countries are expected to agree on a series of 2020 targets to combat the extinctions of plants and animals key to providing clean air and water, medicines and crops.

"Conservation resources are wasted searching for species that have no chance of rediscovery, while most missing species receive no attention," the authors say, pointing to efforts to try to find the Tasmanian tiger.

The last known living Tasmanian tiger, a marsupial hunter the size of a dog, died in 1936 in a zoo.

Fisher told Reuters efforts to find missing species have led to success stories of animals and plants being rediscovered and the creation of protection programs.

But the rediscoveries barely make a dent in the rate of species loss overall, Fisher said by telephone.

"The number of additions every year outweighs the number of that have been redisovered. There's still an accelerating rate of extinctions every year of mammals."

Top photo: An adult male Horton Plains slender loris in an undated photo. The species disappeared from view from 1939 to 2002, leading experts to believe that it had become extinct. Credit: Zoological Society of London / European Pressphoto Agency

Bottom photo: A bridled nailtail wallaby in an undated photo. The bridled nailtail wallaby was thought to be extinct around 1930 but was rediscovered in 1973. Credit: Reuters